This invention is directed to a continuous plasma injector for providing ionized gas into the interelectrode space of a low pressure gas discharge device.
Crossed-field switching devices have been known for many years as laboratory curiosities, as shown in Penning U.S. Pat. No. 2,182,736; and as simple low power devices, as shown in Boucher U.S. Pat. Nos. 3,215,893 and 3,215,939 and Wasa U.S. Pat. No. 3,405,300.
Only recently, however, has the utility of such a switching device in high voltage, high current DC applications been recognized, becuase careful design is necessary for employment of the crossed-field device concept in high current and high voltage situations. Examples of such use are found in Kenneth T. Lian U.S. Pat. No. 3,534,226 and Gunter A. G. Hofmann and Ronald C. Knechtli U.S. Pat. No. 3,538,960.
When onswitching a crossed-field switch device, both an electric field and a magnetic field are applied so that breakdown of the interelectrode gas can take place. This requires an initial electron or ion to start the avalanche. Such particles are always present on a statistical basis due to random cosmic ray events. G. A. G. Hofmann U.S. Pat. No. 3,714,510 also describes the onswitching conditions and employs a plasma puffer to eliminate the wait for the initial particle. Another approach is to use a radioactive source. Another method of creating the necessary ionization is to use a field emitter for electrons, see U.S. Pat. 3,890,520, but field emitters require comparatively high voltage and are subject to sputtering damage. The structure of this invention provides a continuous plasma source using a cold cathode glow discharge employing a thin wire anode.